1. Field of the Invention
This invention is generally directed to a process for stabilizing the appearance of processed fruit fiber and, more specifically, to a process for processing avocado pulp or pulp which has been blended and seasoned into guacamole wherein the pulp or guacamole, prior to packaging, is drawn by vacuum into a chamber wherein the pulp is exposed to a very high vacuum having at least 99% efficiency to thereby remove oxygen from the fruit cells. The high vacuum is maintained on the product for periods of up to 1 minute and thereafter the vacuum is slowly released in order to insure that the chunkiness of the product is maintained. The product is thereafter discharged by gravity into containers after which a second vacuum is applied to the product within the packaging or the head space of the containers purged with steam and inert gas prior to the containers or packages being sealed.
2. History of the Related Art
Processing of fresh avocados into pulp or guacamole is conventionally done in a five step process wherein the fruit is initially washed and thereafter grated to remove culls. The fruit is subsequently peeled and the seed removed after which the pulp is mixed and packaged. Unfortunately, avocado pulp is highly unstable and brooms quickly when exposed to oxygen. The oxygen may be in the surrounding environment or oxygen released from the cells of the pulp as it is mixed. Conventional packaging techniques have relied on simply placing the product, once in a container or package, under vacuum to remove the air trapped in the head space of the container or package. Furthermore, the product is generally exposed to a low vacuum during the packaging process as the product expands and cannot be retained within the containers if too high a vacuum is applied.
Techniques of processing fruit and vegetable fiber by vacuum have been practiced in the fruit preparation art for a period of years. However, the prior art has not appreciated that an extremely high vacuum must be applied to pulp such as avocado pulp and thereafter the pressure slowly stabilized in order to preserve the chunkiness of the product while effectively removing substantially all oxygen from the product cells prior to the product being packaged. Further, the prior art does not recognize a second vacuum step wherein the product within the package or container is also exposed to a high vacuum to thereby insure that no oxygen remains within the container of the packaged product prior to its distribution.
In U.S. Pat. No. 1,421,750 to Willison, a process for treating vegetables in preparation for canning is disclosed wherein vegetables, including asparagus, beans, peas, spinach and the like, are first placed into a vacuum container after which lukewarm water is added. Thereafter, the container is subjected to a vacuum to release air bubbles from the vegetable matter with the air bubbles agitating the liquid and effectively removing mucous substances and impurities from the surface of the vegetables. After the vacuum has been applied the vacuum is "quickly" and "abruptly" broken and the unpurified water removed from the container. Fresh water is added and the sequence is repeated prior to the product being packaged. With this type of process the vegetable matter is placed within a body of water with the body of water being subjected to a vacuum only sufficient enough to cause a bubbling action to release some oxygen from the vegetable product. Further, the vacuum is "abruptly" or "quickly" released which, in the processing of an avocado pulp, would result in possible destruction of the texture of the resulting pulp product.
In U.S. Pat. No. 3,399,999 to Ellett, a process for de-aerating fruits and vegetables is disclosed wherein the product is first cut and thereafter discharged into a rotating vessel wherein the product is, in sequence, mixed with water and held under a partial vacuum until such time as the air within the pores of the slices has been reduced due to a pressure which approximates the partial pressure within the vessel after which the product is discharged through a column of water which is retained at the partial vacuum which, in the preferred embodiment, is described as being between 27 to 28 inches of mercury.
In U.S. Pat. No. 4,014,153 to Wilson, a process for displacing non-condensible gas from voids in food products utilizing fluid displacement techniques is disclosed. In this patent, a product containing non-condensible gases entrapped in voids between the product and in open areas of the product are first placed under vacuum and thereafter water is introduced into the container to displace any entrapped air in the voids in the product and between such products. After the water has been introduced, the air is removed by the vacuum system and the water bled from the degassing chamber.
In U.S. Pat. No. 4,841,850 to Friedmann, a process for treating fruit and vegetable products is disclosed wherein the product fiber is broken down into its smallest possible form by applying high pressure and then releasing the product into a low pressure area so that the elastic limit of the cell walls of the fruit and vegetable fiber is exceeded causing the walls to burst and release their cell contents. A similar process is disclosed in U.S. Pat. No. 4,865,861, also to Friedmann. It should be noted that in both processes the product is initially deaerated prior to being subjected to the high pressure treatment.
In U.S. Pat. No. 4,379,796 to Gross, a method of concentrating fresh fruit is disclosed wherein a mass of fruit is subjected to vacuum pressure sufficient to cause air and liquid in the cells of the fruit to pass through the walls of the cells while also applying temperature to the fruit which is below the boiling point of water at the vacuum pressure being maintained until a major portion of the air in the cells has passed through the walls thereof after which the de-aerated fruit is moved through a vacuum heater to cause liquid from the fruit to coat the surfaces thereof. During the process, the vacuum maintained is generally in the areas of 28.5 inches of mercury or 40.375 mm of pressure. U.S. Pat. No. 4,809,595 to Catelli discloses processing machinery for fruit and vegetable matters wherein the food product is continually processed under reduced atmospheric conditions.
In addition to simply reducing the amount of oxygen associated with processed food products, other prior art processes have incorporated a combination of reducing entrapped air and substituting inert gases such as nitrogen and carbon dioxide into the environment surrounding the processed food product to prevent further oxygenation of the product during its processing and packaging. Some examples of processes that use inert gas in the treatment of processed foods are disclosed in U.S. Pat. Nos. 3,900,571 to Johnson; 4,259,360 to Venetucci et al; and 4,997,664 to Williams.